Enclosed fuse



Nov. 1, 1938. H. T. BUSSMANN ENCLOSED FUSE Filed March 29, 1937 INVENTOR. HEN/P) T BUJZSMA/VN ATTORNEY or... s

Patented Nov; 1, 1938 UNITED STATES ENCLOSED FUSE Henry T. Bussmann, St. Louis, Mo.

Application March 29,

10 Claims.

My invention relates to electricfuses and more particularly to an improvement in the venting of enclosed fuses containing an arcquenching filler.

Among the object of my invention is to provide an enclosed fuse having a simple and emcient system of venting which will permit the pressure to attain a value which will substantially hasten the extinguishment of the are formed on blowing the fuse, and which'will effectively cool the escaping gases.

A further object of my invention is to provide an enclosed fuse having a system of vent-- tained within the enclosure may be very great.

In the case of very heavy overloads, such short circuits, it may be much greater than the enclosure can withstand. c

The pressure inside the casing at any instant depends on the amount of vapor present and on the temperature of that vapor. If, then, the vapor can be cooled and a portion of it condensed as, it is being formed the pressure cannot reach as high a value. As the arc can be carried only by the hotvapors, such cooling and condensation will help in extinguishing the arc. This will lessen the amount of metal vaporized or burned. if some of the uncondensed vapors are allowed to escape from the casing further reduction of pressure will result.

Accordingly by cooling the vapors as formed, condensing a portion of them and allowing the escape of a portion of the uncondensed vapors the pressure may be held within limits which the enclosure can safely withstand.

On the other hand, if the pressure within the fuse be held too low the results may be as undesirable as if it were allowed to become too high. Increased pressure aids in the condensation of the vapors and has a marked effect on extinguishing the are. If the are be allowed to persist so much heat may be generated as to render impossible the proper cooling and condensation of the vapors. Such vapors as may be al- 1937,' Serial No. 133.500 ('01. 200-120) lowed to escape may accordingly be hot enough to ignite nearby combustible material. Holes may be burned in the casing through which flame may escape. The burning may even extend to the fuse terminals and the circuit connections.

An enclosed fuse which will safely protect under all conditions of overload accordingly, should be so designed and constructed that the internal pressure can never reach a value which can endanger the casing. It must, at the same time, permit the pressure to reach a value high enough to quickly extinguish the arc and to maintain the pressure at such value long enough for the arc to be extinguished. It must provide for adequate cooling of such vapors as may be allowed to escape. Fuses embodying my invention are constructed in accordance with these requirements.

For the purpose of quickly cooling and condensing the vapors and to aid in quenching the arc ithas been customary to surround the link with a granular filler of suitable material. The exact size of these granules for best results varies with the design of the link, and the size and design of the enclosure, but as a general proposition the material has some particles larger than others and contains a certain amount of very fine particles; it being desirable to have the filler permit the vapors to pass therethrough and yet be fine enough to condense or absorb a substantial quantity of these vapors.

In cases where the cooling and condensing properties of the filler are insuflicient to prevent the rise of the internal pressure beyond safe limits, it has been common practice .to provide vent holes, or passageways through the walls of the casing, of substantial size, toallow the escape of some of the uncondensed vapors. To prevent leakage of filler screens of fibrous asbestos have been placed before such openings. These materials not only prevented leakage of filler but also tended to restrict the escape of vapors and to cool the escaping vapors more than would the vent holes in the casing alone.

In the drawing Figure l is a view of an enclosed fuse embodying my invention, a part of the casing being cut away.

Fig. 2 is an end view of a closure cap.

Referring to Fig. 1' a fuse link I of any desired design is surrounded by an arc quenching filler 3; both are enclosed in a casing comprising a tubular shell 5 and end closure caps I, which closures may also serve as contact terminals. The link is electrically connected to these closures in any desirable manner, as, for example, by soldering.

A small pin-hole-like vent opening 9 in the end wall of the closure member 1 provides a direct passageway between the interior and the exterior of the casing. It serves as means to permit exit to the open air of some of the vapors generated on blowing the link which have not been condensed or absorbed in passing through the filler.

Fig. 2 shows the vent holes 9 in the end wall of a closure cap 1.

By making the vent hole so small, I restrict the exit of vapors so as to provide definitely a relatively prolonged high pressure within the casing. This pressure is relatively so high and so prolonged that the arc is more quickly suppressed than with lower and briefer pressures. This abrupt extinguishing of the arc prevents more metal being volatilized. Each 1/100 of a second less time required to extinguish the are means that a substantial quantity of metal will not be volatilized and the consequent danger ously high pressures are avoided. I might make this vent hole approximately l/32 inch diameter. Such a size hole is easy to make in the walls of closures of this kind and in many cases serves the purpose very well.

By the use of small vent holes the leakage of filler is prevented. If a hole is used large enough to permit a substantial quantity of the finer par ticles of the filler to sift through, it is necessary to provide a layer of fibrous material such as shredded asbestos, a fabric gauze or a metal screen or a combination of these or similar devices, as is commonly done, to prevent leakage of filler from the vent hole. By my pin-holelike vent the expense of providing and assembling these parts is done away with and more definite results are obtained. Screening of any of the types referred to tends to make uncertain the amount of venting provided, as it will vary with the amount of material used, the tightness of the packing and factors under the control of the operator doing the assembling. By my invention the amount of venting provided is independent of the manner in which the operator assembles the fuse.

By the use of the small vent hole I obtain a still further advantage. The smaller the passageway through which the vapors are allowed to escape the greater will be the proportionate amount of vapor brought in contact with the sides of the passageway. The relatively cool, good conducting sides of the passageway absorb heat from such vapor as comes in contact with them and lower the temperature thereof. Accordingly, other things being equal, the vapors which escape through a small vent hole will be cooler than those which escape through a larger vent. This diminishes the possibility of damage resulting from an excessive temperature of these vapors and, if the holes are small enough, eliminates such possibility.

If a single pin-hole vent does not provide the desired reduction of internal pressure I increase the number of holes as may be required while keeping the size of each hole so small as to cool the vapor and prevent leakage of filler as described. The total venting provided, however, is such that the exit of vapors i's restrictedto a degree which allows a relatively high relatively prolonged pressure to be attained in the casing to aid in quenching the arc. The exact amount of venting desirable cannot be definitely stated in terms of total area of vent holes to be provided because the pressure attained may vary between wide limits without being so high as to endanger the casing or so low as to permit persistence of the arc. The design of the link, the material of which it is made, the kind of material used as filler. the amount of it and the sizes of granules used, and the interior volume of the casing are all among the variables which determine the pressure attained and the pressure desirable. The strength of the casing is another variant which determines the amount of pressure which can safely be permitted. Y From these facts it is clear that a definite formula as to the exact amount of venting required to produce the desired conditions of pressure can not be given.

By the use of the principles of my invention a method is provided for controlling the quenching of the are on blowing an enclosed fuse; for cooling the escaping gases and for ensuring that the amount of venting will be definitely determined. These results can be obtained not only with decrease of cost but with more definite certainty of operation of the fuses.

While I have shown round vent holes in the end walls of the end closures as being a preferred form it is obvious that various modifications in the shape and location of the vent holes may be made within the scope of my invention.

What I claim is:

1. In a cartridge fuse, a casing comprising a. tubular shell and closures at the ends thereof, a fuse link adapted to be mounted within said casing, vapor releasing means extending through the casing, a granular vapor-absorbing filler in the casing in contact with said fuse link and with said vapor releasing means, said vapor releasing means being of such restricted, dimensions as shall practically prevent the leakage of filler therethrough and likewise maintain, within the casing, on blowing of the fuse, a relatively high and prolonged pressure short of that which would endanger the fuse, which relatively high and prolonged pressure will hasten the extinguishment of the arc.

2. In a cartridge fuse, a casing having a tubular shell with metal caps at the ends thereof, a fuse link adapted to be mounted within said casing, a granular vapor-condensing filler in contact with the fuse link, vapor-releasing means extending through said shell or cap and providing an unobstructed passageway between the filler and the exterior of the casing of such restricted dimensions as shall practically prevent the leakage of filler therethrough and likewise maintain, within the casing, on blowing of the fuse, a relatively high and prolonged pressure short of that which would endanger the fuse, which relatively high and prolonged pressure will hasten the extinguishment of the arc.

3. An enclosed fuse including a casing, a fuse link and a granular arc-quenching filler in the casing, vapor releasing means in the casing providing a direct passageway between the arcquenching filler and the exterior of the casing and adapted to permit of a retarded exit of the gases generated on blowing the link and yet substantially prevent the leakage of filler from the casing.

4. An enclosed fuse including a casing, a fuse link and a granular arc-quenching filler in the casing, vapor releasing means in the casing providing a direct passageway between the arequenching filler and the exterior oithe casing and adapted to permit of a retarded exit of the gases generated on blowing the link and yet substantially prevent the leakage of filler from the casing, said vapor releasing means being so designed that the relatively high and prolonged pressure in the casing on the blowing of the fuse will quickly extinguish the arc with less burning of metal occurring than in fuses with large vent holes.

5. In a cartridge fuse, a casing comprising a tubular shell and closures at the ends thereof,

a. fuse link adapted to be mounted within said casing, a granular vapor-absorbing filler in said casing in contact with said fuse link; said casing having an opening extending therethrough providing a direct passageway between the vapor-absorbing filler and the exterior of the easing and of such reduced cross-section as shall practically prevent the leakage of filler therefrom and likewise restrict the exit of vapors pro- I duced on the blowing of the fuse whereby the retarded exit of such vapors will maintain a relatively high and prolonged pressure to promote the condensation of such vapors by the filler without endangering the casing.

6. An enclosed fuse comprising a casing, a fuse link and a granular arc-quenching filler in the casing adapted to condense and absorb a portion of the vapors generated on blowing the link, a passageway of restricted size-through said casing providing a direct passageway between the arc-quenching filler and the exterior of the casing and adapted to prevent the leakage of filler therethrough and to provide an exit for a portion of said vapors at such a'retarded rate as to maintain a relatively prolonged pressure within the casing to aid substantially in extinguishing the arc.

7. An enclosed fuse comprising a casing, a fuse link and an arc-quenching vapor condensing filler in the casing, and passageways in the casing, communicating directly between the interior and the exterior thereof and in contact with said arc-quenching filler, adapted to practically prevent the leakage of filler therethrough and to permit the exit of a portion of the gases generated on blowing the link while at the same time so restricting said exit as to maintain a relatively high relatively prolonged pressure in the casing short of that which would endanger the casing.

8. An enclosed fuse including a casing, a fuse link and an arc-quenching filler in the casing, a passageway approximately 1/32 of an inch in diameter communicating directly between the interior and the exterior of the casing and in contact with said arc-quenching filler, said passageway providing an exit for a portion of the vapors generated on blowing the link and yet so retarding the exit of vapors as to maintain a relatively high and relatively prolonged pressure short of that which would endanger the fuse, whereby the arc is the sooner extinguished.

9. An enclosed fuse including a casing, a fuse link and an arc-quenching filler in the casing, a passageway approximately 1/32 of an inch in diameter communicating directly between the interior and the exterior of the casing and in contact with said arc-quenching filler, said passageway providing an exit for a portion of the vapors generated on blowing the link and yet so retarding the exit of vapors as to maintain a relatively high and relatively prolonged pressure short of that which would endanger the fuse, whereby the arc is so quickly extinguished that the higher dangerous pressures produced in large-vent fuses are avoided and less metal is volatilized.

10. In an enclosed fuse an arc-quenching filler and a metallic end cap having a venting hole therethrough not to exceed one one-thousandth square inch in cross-sectional area and providing a direct passageway from the filler to the exterior of the cap.

HENRY T. BUSSMANN. 

